The invention relates to a housing for installation in motor vehicles to hold electronic components arranged on a PCB, and to the use of such a housing.
In motor vehicles, electronic control systems whose assemblies are accommodated in housings are in increasing use in order to provide protection from the loads and disturbances occurring in operation.
For example, electro-magnetic (EMV) disturbance can have a negative effect on the operation of electronic assemblies. Also, an electronic assembly of this type can itself be the source of such disturbances, which can then have a disturbing effect on other electronic assemblies. To suppress such disturbances, the electronic components are installed in metal housings, designed for example as aluminum die-cast housings, folded housings or extruded housings, or in metallized plastic housings.
At the same time, a metal housing of this type is used for dissipating the heat from the electrical power loss, this being ensured by the additional use of cooling fins at an ambient temperature of -40.degree. C. to +120.degree. C. A metal housing of this type is shown in FIGS. 1 and 2, with FIG. 1 being a plan view of the housing parts and FIG. 2 a section through the housing in accordance with FIG. 1. This housing comprises a frame section 1 and two housing lids 2a and 2b, the frame section 1 being made as an aluminum die-cast housing and the two housing lids 2a and 2b of aluminum. This housing holds the PCB 3, equipped in SMD technology with the electrical SMD components, the power transistors 12, and the plug 11. The plug 11 is connected to the PCB 3 through the holes 5. This fitted PCB 3 is inserted into the frame section 1 as indicated by the arrow 22 in FIG. 1. The PCB 3 is fixed in the frame section 1 by webs 15 and 16 provided in the frame section 1 and having a spacer pin 15a and 16a, respectively, each of which also contains a hole 4 for fastening the PCB 3 using four screws 20. Here, the two webs 15 connect the two longitudinal sides of the rectangular frame section 1 in the area of the edges of the two short sides of the frame section 1. The two other short webs 16 project from one longitudinal side into the frame section 1. Two large-area flange pieces 8 are arranged on the side opposite this longitudinal side. In accordance with FIG. 2, it can be seen that the four webs 15 and 16 each have a spacer pin 15a or 16a, respectively. The PCB 3 rests on these four spacer pins 15a and 16a and is screwed using the screws 20 through the holes 5a in the PCB 3 to the spacer pins 15a and 16a. Here, the power transistors 12 on the edges of the two short sides of the PCB 3 are arranged so that their respective cooling surfaces are in contact with the outer surfaces of the frame section 1. There, on these outer surfaces of the short sides of the frame section 1, cooling fins 10 are provided for improving heat dissipation. Fastening holes 9 are additionally provided on these cooling fins 10. Expanding means 13 are inserted between the power transistors 12 and the webs 15 so that the power transistors 12 are pressed against the outer surfaces of the frame section 1. Finally, the two housing lids 2a and 2b are screwed to the frame section 1 through the holes 19 using screws 21 and 21a. The holes 4a provided on both sides of the frame section 1 are used for this purpose. The frame section 1 has an offset edge 7 on both sides which is used to lock the two housing lids 2a and 2b. Before these housing lids are fitted, a silicone compound is positioned in this edge 7 in order to hermetically seal the housing.
A housing structure of this type as described above has a number of drawbacks. Since the frame section is made using an aluminum die-cast process, the contact surface provided for the PCB 3 by the four spacer pins 15a and 16a has a high degree of evenness. However, the PCB 3 is so distorted by the soldering process that the surface formed by the PCB is no longer even, and so does not correspond to the contact surface. The PCB 3 is now clamped into the contact surface by screwing it there with these spacer pins, with the result that torsional forces now act on it which can be transmitted to the conducting paths and electronic SMD components, so that cracks and breaks cannot be ruled out and may even cause an operational failure. Furthermore, the connecting wires of the power transistors 12 are, due to unfavourable tolerance combinations in the PCB 3 and the frame section 1, subjected by the expanding means 13 to lateral forces which can also cause operational failures.
Finally, assembly of this known housing is difficult due to its many parts and awkward handling, and therefore leads to high production costs.